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Impact of Cyclone Bejisa on sea level in Réunion Island (2 January 2014)

Cyclone Bejisa (2 January 2014) caused a significant rise in sea level in Réunion Island. Two RONIM tide gauges installed in Pointe des Galets and Sainte-Marie de la Réunion measured sea level in real time. The maximum water level measured in Pointe des Galets was 1.58 m above chart datum, and 1.70 m in Sainte-Marie. This height difference is explained by the fact that the maximum level was reached during the high tide in Sainte-Marie. Finally, it should be noted that the maximum storm surge measured by the two tide gauges was identical, approximately 0.70 m.

Tide gauge observations in Pointe des Galets

Pointe des Galets tide gauge observatory (photo credits SHOM, 2011)

Until 9:00 UTC on January 2, the water level data coincided with tidal predictions. After that time and until 22:30, a difference between the observations and the predictions appeared, showing a positive storm surge with water levels up to 0.71 m higher than predicted at rising half-tide. At the forecast high tide (10:02 UTC), the maximum storm surge was about 0.61 m. The maximum water height reached 1.58 m above chart datum or 1.02 m relative to IGN69. For comparison, the highest astronomical tide for this site is 1.01 m above chart datum for Pointe des Galets (according to the Maritime Altimetric Reference Values product 2013 - SHOM).

Observations and predictions of sea level in Pointe des Galets (top graph - heights expressed relative to chart datum) and calculation of storm surges (bottom graph) for 1 to 3 January 2014 during Cyclone Bejisa - Click on the figure to enlarge

Observations of water levels in Sainte-Marie

Sainte-Marie tide gauge observatory (Photo credits SHOM, 2011)

Unlike in Pointe des Galets, the maximum storm surge reached in Sainte-Marie of around 0.75 m coincided with the high tide (around 9:40 UTC on January 2). The maximum water level reached 1.70 m above chart datum in Sainte-Marie.

Observations and predictions of sea level in Sainte-Marie (top graph - heights expressed relative to chart datum) and calculation of storm surges (bottom graph) for 1 to 3 January 2014 during Cyclone Bejisa - Click on the figure to enlarge

Other tide gauge observatories in Reunion Island

Location of tide gauges on Réunion Island (REFMAR Annual Report 2012)

The RONIM tide gauges were not the only ones that observed the sea level during the passage of Cyclone Bejisa. Other devices are installed in Saint-Gilles, Sainte-Rose and Saint-Pierre for the purposes of the Réunion Water Board and the town of Saint-Pierre de La Réunion.